According to Bloomberg, in its statement, the FSB claimed that iPhone maker Apple had been working closely with the NSA for US intelligence purposes. The attacks were said to have involved SIM cards used by diplomats based in Russia, NATO countries, Israel and China.

The report comes shortly after cybersecurity firm Kaspersky published a blog post saying that dozens of its employees' iPhones had been hacked, including technical details about how the hack worked. The incident went undetected for years, and Kaspersky has not identified who was behind what it described as a "highly sophisticated, professionally targeted cyberattack."

In an email, a Kaspersky spokesperson said the hacking campaign was discovered earlier this year and that Russian authorities had found the attacks to be linked. A Kaspersky employee also linked the company’s and the FSB’s claims, saying the spyware worked on older versions of Apple’s operating system.

Kaspersky said the hackers broke into the iPhone by sending a malicious attachment via iMessage. It would work immediately without the user having to click anything. It's a hacking method used by spyware companies, including Israel's NSO Group.

Neither Apple nor the NSA has commented on the report. The incident comes amid heightened tensions between the US and Russia over the Russia-Ukraine conflict. Last month, the US Justice Department announced it had disrupted a years-long hacking campaign run by an FSB unit called Turla. Turla's malware, called Snake, was deployed in more than 50 countries and had been used by the group for more than 20 years, US officials said. The US government also banned Kaspersky software on federal systems in 2017, citing espionage concerns.